Method for mixing and conditioning pulp



Oct. 5, 1943. E. .1. ELLIS ETAL METHOD FOR MIXING AND CONDITIONING PULPOriginal Filed Aug. 10

REAGENT grwe/wboos EDWARDsl-ELL/S JOHN W PAMPL/ V Patented Oct. 5, 1943I UNITED STATES PATENT OFFICE Mimion FOR commoNlNd Edward J. Ellis andJohn Pamplin, Bartow,

Fla, assignors to Southern Phosphate Corporation, Baltimore, Md., acorporation of Delaware Original application August 10, 1938, Serial No.

224,209, now be! 23, 1941.

November 19, 1941, Serial No. 419,786

8 Claims.

The present application is in part a division and in part a continuationof our copending'application for Method for pneumatic flotation, SerialNo. 224,209, filed August 10, 1938.

with the action of the flotation reagent and involves loss of bothreagent and concentratesdestroy the effect of flotation the reagentforms coatings Agitation may also reagents, as where This applicationrelates to apparatus and that are weakly bonded to certain of theparticles, method fol-treating fluid pulps, the term pulp which weaklybonded coatings may be destroyed being used herein to define a mixtureof solid parand dispelled when the pulp is agitated. ticles with aliquid medium. In most fields of mixing pulps it is highly de- Themethod and apparatus of the present insirable that the process becarried onv continuvention are intended primarily for forming pulps 10ously rather than in batches. In certain procand subjecting the formedpulp to such physical treatment as causes a thorough circulation of thefluid medium of the pulp through and among the particles.

The apparatus and method of the invention are particularly adapted fortreating certain types of mineral pulps made from ores, prior tosubjecting them to a flotation process that permits separation ofcertain particle constituents of the pulp from others. In such processesit is'necessary to treat the pulp with selective flotation agents whichhave preferential afiinity for certain of the particles of the pulp andso aflect such particles that separation subsequently can be effected.It

is highly importantthat such flotation reagents be thoroughly dispersedthroughout the pulp, so that it,is brought into intimate contact withsubstantially all of the particles thereof. I Such mixing of the pulpwith the flotation reagents generally is designated conditioning, and isan example of the intimate and thorough type of mixing that the methodand apparatus of this invention are capable ofperforming.

Heretofore such mixing orconditioning of the pulp commonly has beenperformed by means of more or less violent agitation in machines of theimpeller or tumbler type, which operate by agitating the entire body ofpulp, including the solid particles. In such machines, the thoroughnessof the circulation of the fluid medium through and among the solidparticles of the pulp depends upon the violence of the agitation and thelength of the period during which agitation is continued. In certainprocesses violent agitation is detri-- mental. Thus, in the conditioningofthe fines rejected by phosphate washery plants employed to separatethe larger phosphate particles from the raw phosphate rock, which finesare known as phosphate debris, or recovery plant feed, with soaps offatty acids for flotation of the phas 'phate particles, 3, process wellknown in the phosphate 'industry,.violent agitation tends to break downsoft material that normally is present in the debris, and to form acertain amount'oi slimes. The presence of such slimes interferes oofthese reagents exhibit esses speed is essential, for example, the effectof for a period sufliciently long to survive lengthy mixing even whenaccomplished with a minimum of agitation. V

One of the applicants herein has discovered that certain flotationreagents of the so-called cationic type have preferential afiinity forquartz sand over phosphate particles.

this preferential ailinity for quartz only when the proportion ofreagent is rigidly restricted to such limits that the quartz particles'are weakly and temporarily affected. Therefore, when using suchreagents it is important that the entire conditioning procedure becarried out quickly and also with a minimum of agitation. Other cationicreagents which may have a more powerfullyselective afiinity for quartz,and which may therefore be used in larger quantities to provide a morelasting and less easily disrupted effect, are, for reasons of economy,preferably restricted to such proportions as give the more temporary andfragile ef fect.

The present method and apparatus are capable, among other uses, ofconditioning fluid pulps of phosphate debris without harmful 'effect;resulting either from the breaking down oi constituents of the pulp, aswhen soaps of fatty acids are used to render the phosphate particlesfloatable; or-by such agitation or lapse of time,

' or by both agitation'and lapse of time, as will destroy the effect ofthe reagent, as when cationic reagents are used'to condition the quartzsand for flotation.

The above fields of usefulness are given solely by way of example, andthe herein described method and apparatus may be used in any processwhere thorough mixing of a fluid pulp is to be accomplishedcontinuously, and more especially where such mixing is to beaccomplishe'dwith a minimum of agitation of the solid particles, orwhere such agitation should be carried out at high speed.

More specifically, the present invention involves Certain an apparatusand'method for thoroughly, rapidly and continuously mixing a flowingstream of fluid pulp without subjecting it to violent agitation such aswould be detrimental thereto. In obtaining such mixing the pulp issubstantially continuously introduced into a quietly flowing body of thepulp, preferably at one end thereof,

and continuously withdrawn therefrom, while simultaneously disseminatingfine streams ofgas bubbles throughout the body of pulp in a volumesuflicient to cause a thorough circulation of the fluid medium withoutviolent agitation of the solid constituents.

The method of mixing and conditioning pulp will be further described inconnection with the accompanying drawing which shows a preferred form ofapparatus in which the mixing and conditioning may be carried out..However, it is to be understood that such-further description of theapparatus and method is merely by way of arranged in a novel manner foreffecting certain specialized processes; and

Fig. 4 is a perspective view of a flotation device that is peculiarlyuseful in combination with the mixer.

Referring now to the drawing, the mixer comprises an outer,vertically-disposed, substantially cylindrical container or shell 5having an open top surrounded by an'overflow trough 6 formed with aninclined bottom 1. arranged to deliver liquid in the trough to an outletspout 8 arranged at the lowermost point of the bottom 'I.' The lower endof the shell 5 is closed by a porous bottom 9, which may be of canvas orof any other material that will permit gas to pass therethrough infinely disseminated streams. A gas chamber V I II is arranged beneaththe shell 5 so that gas introduced into it under suitable pressure, asby a valved connection H, will be delivered to the interior of the shellthrough the porous bottom 8 in fine streams distributed throughout thecross sectional area of the shell.

An induction pipe I! isarranged to receive pulp delivered to a hopper l3ata level higher than the top edge of the'shell -5 and to conduct it tothe lower portion of the shell. Advanta geously the induction pipe I2 iscylindrical and located centrally of the shell 5, so that an annularspace II is formed between the inner surface of the shell and the outersurface of the induction pipe l2. However, the essential arrangement ofthe induction pipe relative to the shell is that its bottom edge beadjacent but spaced from the bottom 9 of the shell, and that sufiicientspace be present ,within the shell and outside of the pipe for upwardflow of the stream of pulp in a smooth, non-turbulent manner.

.In operation the fluid pulp .is continuously fed to the hopper I: fromwhich it flows downwardly through the pipe l2 and is delivered tothe'space I 4 through which it flows upwardly in a gently and quietly'fiowing stream until it overflows at the top of'the shell 5 into thedelivery trough 6.

I Gas is continuously supplied to the chamber I0 under suflicientpressure to cause it to pass through the porous bottom 9 and into thestream of pulp, where it forms fine bubbles 'that rise in the flowingpulp stream and causes the liquid medium of the pulp to circulate amongthe solid particles and causes a thorough dispersion and mixture of thefluid medium among such particles.

The phosphate debris which remains after crude phosphate pebble ore hasbeen subjected to washing and classifying operations has a free slimecontent of about 0.5% to 5.0% by weight and a particle size rangingsubstantially from plus 100 mesh to minus 20 mesh. Phosphate rock ispresent in such debris to the extent of about 5-35%, and quartz sand tothe extent of about 80-50%. There is also usually some clay present bothas particles, and adhering to the other particles in the nature ofcoatings.

As indicated above, and as is commonly known, the phosphate particlesmay be floated from the quartz by use of anionic reagents; such as soapsof fatty acids, which ordinarily are used with inert oily materials topromote agglomeration. In such cases the debris may be used as it comesfrom the washery. Asis also indicated above, cationic reagents may beused to render the quartz 'sand particles floatable from the phosphate.In such case, it is advisable to break down the easily slimablematerial, such as clay or other soft substance present in the debris,and remove it .from the debris prior to adding the flotation reagent,as'sucli materials interfere very seriously with the action of theflotation reagent.

Fig. 3 illustrates a plant including the abovedescribed mixer which ispeculiarly suited for recovery of the phosphate content of phosphatedebris. The debris is fed to the mixer, designated IS, in the form of afluid pulp, a water content of about 40% producing a suitable degree offluidity. The flotation reagent, of either cationic or anionic type,together with the inert oily material, if the latter is used; and anyother desirable reagent is added to the pulp from a feeder,advantageously arranged to deliver to the hopper i3 into which the pulpis fed. As the pulp, after passing downwardly through the induction pipei2, flows upwardly through the space I 4, gas bubbles rising from theporous bottom 9 gently agitate the. fluid medium of the pulp, causingsuch medium, and with it the reagent, to circulate through the pulp andflow between the solid particles thereof, dispersing the reagentthoroughly throughout the flowing pulp stream and bringing the reagentinto-contact with substantially every solid'. particle. As the risinggas bubbles move quite gently and are of small weight compared with thesolid particles, they tend to pass around the particles without movingthem viole'ntly or to any great degree. The particles therefore are notagitated with sufllcient violence to set up attrition between them, andconsequently harmful effects that may be caused by attrition, such Whenthe top of the shell is reached the pulp,

as. breaking or abrasion of the particles, or dis.-

pelling of reagent coatings from them, are subbeing then thoroughlyconditioned, overflows into the trough 6 and is delivered by the spout 8to a separation device H, which may be of any a head wall 20 and an opendelivery end 2|. The

trough is inclined from the head to the delivery end at a degree thatprovides a rapid flow of the pulp and that prevents sedimentationthereof upon the porous bottom. A gas chamber enclosed by walls 22underlies the porous bottom so that gas supplied thereto under suitablepressure will pass upwardly into the stream of pulp flowing through thetrough in finely divided streams that rise in the stream of pulp byreason of their own buoyancy. The water-repellent particles that havebeen afiected by the selective reagent used to condition the pulp areraised to the upper portions of the stream by the air bubbles, while theunaifected, water-wett-able particles sink and are carried along in thelower portion of the stream. The upper portion of the.

stream, containing the bulk of the reagentafiected particles, togetherwith any froth that may be floatingon the surface of the stream, areintercepted and diverted from the stream through openings 24 to adelivery launder 22 by 'skimmers 23 spaced along the trough.

It will be seen that in the plant arrangement just described, the fastand gentle action of the mixer is continued by the particular separationtrough disclosed in Fig. 4, so that the entire process is continuous,free from agitation and of such nature as to produce no violentagitation or attrition between the solid particles of the pulp, andisfalso very fast.

In utilizing cationic reagents, we regard it as preferable to so controlthe speed of the pulp stream with relation to the depth of the shell ofthe mixer, and to so arrange the inclination of the separation troughthat the entireprocess ofmixing and conditioning the pulp and separatingthe constituents thereof is completed within oneminute from theintroduction of the pulp to the hopper of the mixer. By inclining theseparating trough to such a degree that the speed of the flow through itis of the order of 100 feet per minute the separation may beaccomplished inabout. five seconds from the delivery of the pulp to thetrough. Thorough conditioning may be accomplished by use of the bubbletype mixing herein disclosed within a period of about 45 seconds, whichperiod is of such length that at its expiration the cationic reagentwill be fully effective.

What we claim is:

l. The method of dispersing a flotation. reagent throughout a pulp ofsolid particles and a liquid medium preparatory to selective separationof constituents forming the solid particles of the pulp, which comprisesintroducing the pulp and the reagent to be dispersed therein into amixing zone'in which pulp is flowing upwardly, introducing finelydisseminated gas bubbles to pass upwardly through the body of pulp inthe mixing zone at a speed greater than the upward speed of the pulp andin suillcient volume to keep the solid particles of the pulp insuspension and to cause an upward movement of the liquid medium betweenand about the solid particles of the I portion of the body of the pulp.

2. The method of dispersing a flotation reagent throughout a pulp ofsolid particles and a liquid medium, preparatory to selective separationof constituents forming the solid particles of the pulp, which comprisessubstantially continuously introducing the pulp and-the reagent to" bedispersed therein into thelower portion of a quietly flowing body of thepulp, introducing finely disseminated gas bubbles to pass upwardlythrough the flowing body of pulp in sufiicient volume to keep the solidparticles of the pulp in suspension and to cause an upward movement ofthe liquid medium between and about the solid particles of the pulp sothat the reagent is substantially uniformly dispersed throughout theflowing body of pulp and is brought into contact with the solidparticles thereof, the volume of air being insuflicient to agitate'thesolid particles of the pulp with sufiicientwiolence to cause attritionbetween them, such as would cause appreciable. breaking or abrasion ofthe particles, or an appreciable dispelling of reagent coatings fromthem, and substantially continuously removing the pulp and dispersedreagent as an unseparated, intimate mixture from the upper portion of.the body of pulp at a rate substantially equal to that at which thepulp was introduced.

3. The method of dispersing a flotation reagent throughout a pulp ofsolid particles and a liquid medium, preparatory to selective separationof constituents forming the solid particles of the pulp, which comprisesintroducing the pulp and the reagent to be dispersed therein into aquietly flowing body of the pulp, introducing.

finely disseminated gas bubbles to pass upwardly through the quietlyflowing body of the pulp in suflicient volume to keep the solidparticles of the pulp in suspension and to cause an upward movement ofthe liquid medium between and about the solid particles of the pulp sothat the is substantially uniformly dispersedreagent throughout theflowing body of pulp and is brought into contact with the solidparticles thereof, the volume of air being insuficient to agitate thesolid particles of the pulp with sufficient violence to cause attritionbetween them,

such as would cause appreciable breaking or abrasion of the particles oran appreciable dispelling of reagent coatings from them, andsubstantially continuously removing the pulp and dispersed reagent as anunseparated, intimate mixture.

4. The method of dispersing a flotation re-I agent throughout a pulp ofphosphate debris and a liquid medium, preparatory to selectiveseparation of constituents forming the phosphate debris, which comprisesintroducing the pulp and the reagent to be dispersed therein into aquietly flowing body of pulp, introducing finely disseminated gasbubbles to pass upwardly through the body of pulp in suflicient volumeto keep the parpension and to cause upward movement. of the liquidmedium about the particles of the phosphate debris so that the reagentis substantially uniformly dispersed throughout the flowing body 01' thepulp and is brought into contact with the particles of the phosphatedebris, the volume of, air being insuflicient to .agitate the particlesof the phosphate debris of the pulp with suflicient violence to causeattrition between them, such as would cause appreciable breaking orabrasion of such particles, o1 an appreciable dispelling of reagentcoatings from them, and substantially continuously removing the pulp anddispersed reagent as an unseparated, intimate mixture.

5. The method of dispersing a selective flotation reagent throughout apulp of phosphate debris and a liquid medium, preparatory to selectivesepa ration of constituents of the phosphate debris which comprisesintroducing .the pulp and the reagent to be dispersed therein into aquietly flowing body of the pulp, i'ntroducingflnely disseminated gasbubbles to pass upwardly through the body of the pulp in sumcient volumeto keep the particles of the phosphate debris in suspension and to causean upward movement ofthe liquid medium between and about them so that,the reagent is substantially uniformly dispersed throughout the flowingbodyof the pulp andis brought into contact with the particles of thephosphate debris, the volume of air being insui'-.

ficient to agitate the particles of the phosphate debris with'sufficient violence to cause attrition between them, such as wouldcause appreciable breaking or abrasion of the particles, or anappreciable dispelling of reagent coatings from them, and substantiallycontinuously removing the pulp and dispersed reagent as an unseparated,intimate mixture at a rate substantially equal to that at which the pulpand reagent were introduced into the body of pulp.

6. The method of dispersing a flotation reagent throughout a pulp ofphosphate debris and a liquid medium, preparatory to selectiveseparation of constituents of the phosphate debris, which comprisessubstantially continuously introducing the pulp and the reagent to bedispersed therein into the lower portion of a'mixing zone in which thepulp is flowing upwardly, introducing flnely disseminated gas bubbles topass upwardly through the body of pulp in the mixing zone at a speedgreater thanv the upward speed of the pulp and in suiflcientvolume tokeep the phosphate debris particles thereof in suspension and'to causean upward movement of the liquid I medium between and about theparticles of the phosphate debris so that the reagent is substantiallyuniformly dispersed throughout the body of pulp and is brought intocontact with the particles of the phosphate debris, the volume of airbeing insufllcient to agitate the particles of the phosphate debris with'suflicient violence to cause attrition between them, such as wouldcause appreciable breaking or abrasion of the'particles, or anappreciable dispelling oi. reagent coatings from them, andfsubstantiallycontinuously-rem'ovingthe pulp and dispersed reagent as an unseparated,-intimate mixture from the upper por-. tion of said mixingzone at a rate substantially equal to that at which the pulp and reagentare introduced into the lower portion of the mixing zone, the rate ofintroduction and withdrawal of the pulp from said body being such thatintro- 5 duced pulp remains in said body for. a period of time notsubstantially exceeding one minute.

, 7. The method of dispersing a flotation reagent throughout a pulp ofphosphate debris and a liquid medium, preparatory to selectiveseparation of constituents forming the solid particles of the pulp,which comprises substantially contintion reagent which has apreferential aflinity for quartzsand over phosphate'particles and forms5 weakly bonded coatings thereon into the lower portion of a quietlyflowing-body of such pulp, introducing flnely disseminated gas bubblesto pass upwardly through the quietly flowing body of pulp in sufllcientvolume to keep the particles 0 of phosphate-debris of the pulp insuspension and to cause an upward movement of theliquid medium betweenand about the particles of the phosphate debris so that the reagent issubstantially uniformly dispersed throughout the body of pulp and isbrought into contact with the par ticles'of the phosphate debris,thevolume of air being insuilicient to agitate the particles of phosphatedebris with suflicient violence to cause attrition between them, such aswould cause appreciable breaking or abrasion of the particles, or anappreciable dispelling of liquid coatings from them, and substantiallycontinuously removing the pulp and dispersed reagent as an unseparated,intimate mixture fromthe upper portion of the body of pulp at a ratesubstantially equal to that at which the pulp and reagent are introducedinto the lower portion thereof, the rate of introduction and withdrawalof pulp from the mixing zone being sueh that introduced pulp re- 40mains in said body for a period of time not substantially exceeding oneminute. 7 8. The method 01. dispersing a flotation reagent throughout apulp of solid particles and a liquid medium preparatory to selectiveseparation of constituents forming the solid particles of the pulp,which comprises introducing the pulp and the reagent to be dispersedtherein into the quietly flowing body of the pulp, introducing finelydisseminated gas bubbles throughout substantially the entirecross-sectional area of the body of pulp in the mixing zone insufllcient volume to keep the solid particles oi! the pulp in suspensionand to cause a circulation of the liquid medium between and about thesolid particles of the pulp so that the reagent is substantiallyuniformly dispersed throughout thebody of pulp and is brought intocontact with the solid particles thereof, the volume of air beinginsuflicient to agitate'the solid particles of the pulp tween them, suchas would cause appreciable EDWARD J. JOHN w. PAMPLIN.

uously introducing the pulp and a selective flotawith sufllcientviolence to cause attrition be-

